1. Field of the Invention
This invention relates to a positive type radiation-sensitive resist composition which is sensitive to radiation such as ultraviolet rays, far ultraviolet rays including excimer laser and the like, ion beam, X ray, and the like.
2. Description of the Related Art
Hitherto, integrated circuits have been produced according to the mask contact printing method. However, the mask contact printing method is disadvantageous in that a finely fabricated mask is difficult to prepare and resolution of the process cannot exceed 2 .mu.m. For this reason, the reduced projection process exhibiting a resolution of sub-micron order is mainly used today in its place. However, the reduced projection process is disadvantageous in that the total exposure time per sheet of wafer is long, and improvement of resist sensitivity is necessary in order to solve this problem. If the exposure time can be shortened by improving the sensitivity of the resist, the through-put can be improved and thereby the yield of integrated circuits can be increased.
On the other hand, due to the increase in the degree of integration in integrated circuits (particularly LSI), the width of wiring has been lessened more and more, as a result of which the method of dry etching has been adopted in addition to the prior wet etching method. In the dry etching method, the resist is required to have a higher level of heat resistance (dry etching resistance) than in the prior methods.
In order to enhance the sensitivity of the resist, a method of lessening the molecular weight of the alkali-soluble resin is generally adopted. However, this method is disadvantageous in that the so-called .gamma. value which is dependent on the difference in dissolution velocitives of the unexposed areas into a developing solution are lowered, the resolution is lowered, the heat resistance of the resist is lowered, and the adhesion between resist the and the substrate is lowered. As improvement in one of these performances brings about a deterioration in another performance, it has been very difficult to prepare the positive type resist composition having the excellent performances, such as resolution, sensitivity and heat resistance.